gas-phase photocatalytic oxidation of volatile organic ... - Doria

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4 TBA proceeded faster in humid air than dry air. MTBE oxidation, however, was less sensitive to humidity. The TiO2 catalyst was stable during continuous PCO of MTBE and TBA above 373 K, but gradually lost activity below 373 K; the catalyst could be regenerated by UV irradiation in the absence of gas-phase VOCs. Sulphur dioxide, carbon monoxide, carbon dioxide and water were identified as ultimate products of PCO of ethanethiol. Acetic acid was identified as a photocatalytic oxidation by-product. The limits of ethanethiol concentration and temperature, at which the reactor performance was stable for indefinite time, were established. The apparent reaction kinetics appeared to be independent of the reaction temperature within the studied limits, 373 to 453 K. The catalyst was completely and irreversibly deactivated with ethanethiol TCO. Volatile PCO products of MA included ammonia, nitrogen dioxide, nitrous oxide, carbon dioxide and water. Formamide was observed among DMA PCO products together with others similar to the ones of MA. TCO for both substances resulted in the formation of ammonia, hydrogen cyanide, carbon monoxide, carbon dioxide and water. No deactivation of the photocatalyst during the multiple long-run experiments was observed at the concentrations and temperatures used in the study. PCO of MA was also studied in the aqueous phase. Maximum efficiency was achieved in an alkaline media, where MA exhibited high fugitivity. Two mechanisms of aqueous PCO – decomposition to formate and ammonia, and oxidation of organic nitrogen directly to nitrite - lead ultimately to carbon dioxide, water, ammonia and nitrate: formate and nitrite were observed as intermediates. A part of the ammonia formed in the reaction was oxidized to nitrite and nitrate. This finding helped in better understanding of the gasphase PCO pathways. The PCO kinetic data for VOCs fitted well to the monomolecular Langmuir- Hinshelwood (L-H) model, whereas TCO kinetic behaviour matched the first order process for volatile amines and the L-H model for others. It should be noted that both L- H and the first order equations were only the data fit, not the real description of the reaction kinetics. The dependence of the kinetic constants on temperature was established in the form of an Arrhenius equation. Keywords: photocatalysis; thermal catalytic oxidation; air treatment; semiconductor; photocatalyst lifetime; 2-methoxy-2-methylpropane; tert-butanol; ethyl mercaptan; monomethylamine; N-methylmethanamine UDC 628.16.094.3 : 544.526.5 : 628.316.7
ACKNOWLEDGEMENTS 5 The author gratefully acknowledges the Academy of Finland, the Graduate School in Chemical Engineering, Finland, the Maj and Tor Nessling Foundation, the Research Foundation of Lappeenranta University of Technology, and the Estonian Science Foundation for financial support of the research. The author would like to express her deepest gratitude to her supervisor, Dr. Sergei Preis for fruitful discussions and sharing his academic knowledge, for his constant support during the last seven years of our productive collaboration. I also would like to thank Prof. Juha Kallas for his encouragement and support. There is also my exceptional gratitude to Dr. Marina Krichevskaya for her teaching talent: she guided me through the early study of PCO principles, making the subject clear not only in detail but also sharing her overall scientific experience in chemical engineering. Special acknowledgments are given to my mother and all my friends for their continuous direct and indirect support, patience, understanding and encouragement throughout the different stages of this work. Lappeenranta, November 2007 Anna Kachina
Page 1 and 2: Anna Kachina GAS-PHASE PHOTOCATALYT
Page 3: ABSTRACT Anna Kachina Gas-phase pho
Page 9 and 10: LIST OF PUBLICATIONS 7 The present
Page 11 and 12: 1 INTRODUCTION 9 Substances emitted
Page 13 and 14: 11 oxidation (TCO) experiments were
Page 15 and 16: 1.2.3 Amino compounds 13 The chemic
Page 17 and 18: 15 The commercialization of TiO2-ba
Page 19 and 20: 17 polymer matrix (Brezová et al.,
Page 21 and 22: 19 ambient temperatures. However, s
Page 23 and 24: 2.3 Reaction kinetics 21 The L-H mo
Page 25 and 26: 3 RESULTS AND DISCUSSION 3.1 Experi
Page 27 and 28: 3.2 Catalyst life-time and reaction
Page 29 and 30: Table 3.2.1 Catalyst deactivation t
Page 31 and 32: 29 Table 3.3.1 Reaction rate consta
Page 33 and 34: 31 Table 3.4.1 Arrhenius equation p
Page 35 and 36: References 33 Aguado, J., Grieken,
Page 37 and 38: 35 Fernández, A., Lassaletta, G.,
Page 39 and 40: 37 Lee, S. H, Kang, M., Cho, S. M.,
Page 41 and 42: 39 Sabate, J., Anderson, M. A., Agu
Page 43: 41 APPENDICES

gas-phase photocatalytic oxidation of volatile organic ... - Doria

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